I don't know why people think "Blaine" was a fan mistranslation. If anything, "Brain" was an SENA mistranslation. The "l" is replace with "r" in Japanese-spoken English words because that's the style. If the original was "Bu-rain-u" or something like that, then it would be natural that the English translation was "Blaine". Again, "Brain" was probably another SENA translation error (right Roxas).

Maybe they can be both correct translations, because in japanese Blaine and Brain sound the same? I don't know japanese, I'm just guessing, but if this is the case then there's no mistake, just a choice they made.

Just like in Kingdom Hearts HD 1.5 ReMIX, upon completion of a title in Kingdom Hearts HD 2.5 ReMIX you unlock a custom PlayStation 3 theme. Kingdom Hearts HD 2.5 ReMIX contains Kingdom Hearts II Final Mix,Kingdom Hearts Birth by Sleep Final Mix and Kingdom Hearts Re:coded. In order to unlock Kingdom Hearts II Final Mix's you must simply complete the game. For Kingdom Hearts Birth by Sleep Final Mix, you must complete the Final Episode. And lastly for Kingdom Hearts Re:coded you must complete the title 100% by watching all of the Cinematic Story Videos and viewing the Character Profiles. Their custom themes can be viewed below thanks to Everglow.